Oxidative desulfurization of sulfur-containing hydrocarbons

ABSTRACT

A method for desulfurizing a hydrocarbon stream ( 10 ) containing heterocyclic sulfur compounds, which process comprises contacting the heterocyclic sulfur compounds in the gas phase ( 60 ) in the presence of oxygen ( 70 ) with a supported metal oxide catalyst, or with a bulk metal oxide catalyst ( 600 ) to convert at least a portion of the heterocyclic sulfur compounds to oxygenated products as well as sulfur-deficient hydrocarbons and separately recovering the oxygenated products separately from a hydrocarbon stream with substantially reduced sulfur.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provision application Ser.No. 60/339,162.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention broadly relates to a process for the removal andsubsequent conversion of sulfur compounds found in hydrocarbons,especially refractory sulfur compounds found in petroleum streams (blendstocks) used to make gasoline and diesel fuel, to useful oxygenatedhydrocarbon products and sulfur dioxide. Thus, the invention broadlyrelates to producing a hydrocarbon stream of a lowered sulfur content.The invention particularly relates to a catalytic gas phase oxidationprocess using a supported metal oxide catalyst or a bulk metal oxidecatalyst for treating refractory sulfur compounds found in petroleumstreams, such as used to make gasoline and diesel fuel, and convertingthem to useful oxygenated hydrocarbon products, such as maleic acid(anhydride), phenol, benzyl aldehyde and benzoic acid, and to sulfurdioxide. This method can also be extended to the removal of sulfurtypically present in such sulfur containing hydrocarbons as gasoline anddiesel fuels to yield sulfur dioxide and sulfur-deficient hydrocarbons.

2. Description of Related Art

Diverse types of petroleum feedstocks and streams contain sulfurcompounds whose removal often is indispensable for commercialutilization of the feedstock or stream and/or for subsequent processingof the feedstock. In the face of ever-tightening sulfur specificationsin transportation fuels, such as gasoline and diesel fuel, sulfurremoval from petroleum feedstocks used to makes such fuels and from thepetroleum fuel products themselves will become increasingly moreimportant in years to come. In this regard, there have been severalstudies by the EPA concluding that the presence of sulfur in gasolinehas an adverse impact on catalytic converters and, thus, tailpipeemissions from automobiles.

Sulfur deactivates conventional three-way Pt/Pd/Rh/Al₂O₃ catalyticconverters designed to reduce hydrocarbon, CO and NOx emissions. Sulfuralso degrades automobile diagnostic systems. Gasoline sulfur alsoprevents the introduction of more advanced catalytic technologies, suchas Pt/BaO-based catalysts as NOx traps. For diesel fuels, the presenceof sulfur produces an additional problem since particulate emissionscreated during combustion are increased in the presence of sulfur. Thereis special concern for particulates less than 2.5 microns since the EPAhas concluded that there is a stronger link than ever between thetiniest soot particles and thousands of premature deaths each year.Consequently, both the EPA and the DOE have recommended thatsignificantly limiting the level of sulfur in gasoline (15 ppm) anddiesel fuels (30 ppm) would be essential for meeting lower vehicleemission standards in the future (by 2007). It is no surprise thatsubstantial efforts have been expended to eliminate sulfur compoundsfrom petroleum products.

Sulfur compounds routinely found in petroleum feedstocks and productsinclude thiols (RSH), sulfides (RSR), disulfides (RSSR), saturatedcyclic sulfides (C₂-C₅-cyclic sulfur-compounds, which incorporate sulfurinto the saturated ring structure), thiophenes (primarily unsaturatedC₄-cyclic sulfur compounds, where sulfur is incorporated into theunsaturated ring structure) and thiophene derivatives such asbenzothiophene and dibenzothiophene (benzene rings that are fused to thesides of the thiophene (unsaturated C₄-cyclic sulfur compound) andvarious substituted benzothiophenes and dibenzothiophenes. Sulfur is themost abundant heteroatom impurity in petroleum crude and varies from 0.1to 5 wt % depending on the geographic origin of the petroleum. Afterdistillation of the crude oil, the sulfur content increases with thefraction's boiling point: naphtha (0.01-0.05% sulfur), kerosene(0.1-0.3% sulfur), gas oil (0.5-1.5% sulfur), atmospheric residue(2.5-5% sulfur), vacuum gas oil (1.5-3% sulfur), and vacuum residue(3-6% sulfur).

For the low boiling naphtha fraction, sulfur is mainly present asthiols, sulfides, disulfides or thiophene. For the middle boilingkerosene and gas oil fractions and especially the higher boilingfractions, thiophenic compounds, particularly benzothiophenes, dominate.

As a general rule, simple aliphatic, naphthenic, and aromaticmercaptans, sulfides, di- and polysulfides and the like surrender theirsulfur more readily than the class of heterocyclic sulfur compoundscomprised of thiophene and its higher homologs and analogs. Within thegeneric thiophenic class, desulfurization reactivity decreases withincreasing molecular structure and complexity. While simple thiophenesrepresent the more labile sulfur types, the other extreme, sometimesreferred to as “hard sulfur” or “refractory sulfur,” is represented bythe derivatives of benzothiophene and dibenzothiophene, especially thosemono- and di-substituted and condensed ring dibenzothiophenes bearingsubstituents on the carbons beta to the sulfur atom. These highlyrefractory sulfur heterocycles resist desulfurization.

Conventional technology removes sulfur from petroleum feedstocks viacatalytic hydrodesulfurization (HDS). Hydrodesulfurization is one of thefundamental processes of the refining and petrochemical industries. InHDS, sulfur removal is typically achieved by reaction of the sulfurcompounds with hydrogen over non-noble metal sulfides, especially thoseof Co/Mo/Al₂O₃ and Ni/Mo/Al₂O₃ catalysts, operating at elevatedtemperatures (˜400° C.) and extremely high pressures (˜100 atmospheres).Under these somewhat severe reaction conditions, (1) RSH, RSR and RSSRreact to form hydrocarbons (RH), (2) saturated cyclic sulfides areconverted to alkanes, (3) thiophene reacts largely to mixed isomers ofbutene (C₄H₈), (4) benzothiophene and its derivatives are initiallyhydrogenated to thiophane derivatives before removal of the sulfur atomto finally yield ethylbenzene (Bz-CH₂CH₃) and (5) dibenzothiophene ismainly converted to biphenyl with small amounts of phenylcyclohexene.The sulfur itself, along with the H₂, is ultimately converted tohydrogen sulfide. This H₂S is subsequently reacted with O₂ in the Clausprocess to H₂O and elemental sulfur, which is disposed in speciallandfills. An overall hydrogen balance for the HDS process reveals thatthe very valuable and expensive H₂ ultimately gets converted toinvaluable H₂O.

Hydrogen consumption, thus, is an important consideration in thesehydrodesulfurization (HDS) reactions because many of the componentspresent in the feedstocks are more valuable as unsaturates, especiallyaromatics and olefins, and the hydrogenolysis of such components resultsin the production of light gases with marginal fuel values. In addition,during the manufacture of H₂ a significant amount of global warming CO₂is generated during the very energy intensive steam reforming ofmethane, or steam reforming of lower hydrocarbons. The H₂ is typicallygenerated by steam reforming of CH₄, or lower hydrocarbons, and thewater-gas shift reaction as follows:CH₄+H₂O⇄CO+3H₂CO+H₂O⇄CO₂+H₂.

Thus, the current HDS process technology converts valuable H₂ toinvaluable H₂O, reduces the octane of the gasoline feedstocks, generatesglobal warming CO₂ and elemental sulfur that needs to be disposed and isextremely energy intensive.

Notwithstanding these drawbacks, the petroleum industry has stated thatHDS will be the preferred approach they will use to reduce sulfur levelsin response to tighter regulatory controls because, HDS is awell-established and proven technology.

While HDS, as currently practiced, is known to provide nearly completeremoval of mercaptans, sulfides and disulfides from liquid hydrocarbons,use of the current designs for reducing the level of thiophenes andother refractory sulfur compounds to a level of 30 ppm or below isproblematic. In order to meet this very low level of sulfur, petroleumrefiners will have to build additional capacity for generatingadditional hydrogen and will have to increase the reactor capacities oftheir HDS units or develop significantly more active HDS catalysts.Furthermore, efforts to drive the current HDS processes to increasedsulfur removal is likely to lead to increased hydrogenation of thevaluable fuel components and degradation in the fuel value (octanereduction) of the treated petroleum feedstock.

While HDS remains the predominant commercial approach for desulfurizingpetroleum products, particularly petroleum feedstocks for makinggasoline, the prior art has continued to develop and examine alternativeprocesses. For example, various oxidative processes are known forremoval of mercaptans by converting them to disulfides; such as theMerox™ process (see Handbook of Petroleum Refining Processes, R. A.Meyers, editor-in-chief, chapter 9.1, McGraw-Hill Book Company (1986)).It is also known to remove mercaptans and disulfides from petroleumfeedstocks by adsorption with clays. U.S. Pat. No. 5,360,536 uses anadsorbent of a solid solution of metal oxides.

U.S. Pat. No. 5,935,422 describes a process for removal of organicsulfur compounds, particularly heterocyclic sulfur compounds, frompetroleum feedstocks, and especially FCC feedstocks, by adsorption usingzeolite Y exchanged with an alkali or alkaline earth metal cation andpreferably impregnated with a group VIII metal. Regeneration of thesorbent is achieved by beating the sulfur-laden adsorbent in a hydrogenatmosphere.

The prior art also is exploring the use of biological removal processes(biodesulfurization). For example, U.S. Pat. No. 6,130,081 relates to amethod of degrading organic sulfur compounds such as benzothiophene,dibenzothiophene and the like, by use of microorganisms belonging to thegenus Paenibacillus and having the ability to decompose organic sulfurcompounds, especially heterocyclic sulfur compounds, by specificallycleaving their C—S bonds under elevated temperature conditions.

Te et al., “Oxidative reactivities of dibenzothiophenes inpolyoxometalate/H₂O₂ and formic acid/H₂O₂ systems,” Applied Catalysts A:General, 219(2001) 267-280 describes a liquid phase oxidation processpotentially useful for removing refractory sulfur compounds from liquidhydrocarbon feed steams. The sulfur compounds are oxidized to sulfonesand sulfoxides, which then can be extracted from the hydrocarbon. Otherliquid phase oxidative approaches are described in EP 565 324 and U.S.Pat. No. 5,910,440 (biocatalytic).

I. G. Fedorchenko, N. N. Nechiporenko, V. I. Mitryaeva and E. N.Dubranovskaya, “Catalytic Activity of Certain Metal Oxides in Oxidationof Sulfur Compounds,” Vesten. Khar'kov. Politekh. Inst. 13 (1966):44-47describes work involving the oxidation of thiophene over active metaloxides mixed with pumice, 1/4 ratio. Best results were obtained withFe₂O₃, MoO₃ and Al₂O₃, but the reaction products obtained under thechosen reaction conditions were CO_(x), SO₂ and H₂O. A similarcombustion study of thiophene was reported by V. A. Sslavinskaaya, D.Kreile, D. Eglite and I. Geimane, “Formation of Carbon Monoxide andCarbon Dioxide in the Vapor-Phase Oxidation of Heterocyclic Compounds onVanadium-Molybdenum-Phosphorous Catalysts,” Latv. PSR Zinat. Akad.Vestis, Kim. Ser. 6 (1971): 735-738. These investigators employed aV—Mo—P catalyst.

Another interesting investigation of thiophene oxidation over a 10% MoO₃and TiO₂ mixed metal oxide catalyst is reported by M. Blanchard and J.Goichon, “Heterogeneous Catalytic Oxidation of Aromatic SulfurCompounds: Thiophene and Benzothiophene,” Bull. Soc. Chim. Fr. 1-2/Pt. 2(1975): 289-290. The oxidation yielded 75% selectivity towards maleicanhydride and thiomaleic anhydride at moderate conversions. SupportedMoO₃/TiO₂ and bulk V₂O₅ were also found to be efficient catalysts forthe selective oxidation of thiophene to maleic products. In addition,oxidation of benzothiophene over the 10% MoO₃—TiO₂ catalystquantitatively yielded phenol with 100% selectivity.

U.S. Pat. No. 5,969,191 describes a catalytic thermochemical process,which can be used for converting by-products from pulp and paper mills(TRS compounds including mercaptans) to a valuable chemical intermediate(H₂CO), which is consumed in the pulp and paper Industry. A keycatalytic reaction step in the thermochemical process scheme is theselective catalytic oxidation of organosulfur compounds (e.g.,CH₃SH+2O₂→H₂CO+SO₂+H₂O) over certain supported (mono-layered) metaloxide catalysts. The preferred commercial catalyst employed in thisprocess consists of a specially engineered V₂O₅/TiO₂ catalyst thatminimizes the adverse effects of heat and mass transfer limitations thatcan result in the over oxidation of the desired H₂CO to COx and H₂O.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a process of the present invention.

FIG. 2 is another schematic drawing of a process of the presentinvention.

FIG. 3 is still another schematic drawing of a particularly preferredprocess of the present invention.

FIG. 4 illustrates the results of Temperature Programmed SurfaceReaction-Mass Spectrometry experiments.

FIG. 5 illustrates another result of the Temperature Programmed SurfaceReaction-Mass Spectrometry experiment.

BRIEF DESCRIPTION OF THE INVENTION

The present invention is directed to a process for removing sulfurcompounds found in a hydrocarbon stream, e.g., in a petroleum feedstockor petroleum product, and converting such sulfur compounds, or sulfinyl(═SO) or sulfonyl (═SO₂) derivatives thereof, to sulfur dioxide and touseful oxygenated products as well as sulfur-deficient hydrocarbons byvapor phase oxidative desulfurization of the sulfur compounds, or thesulfinyl (═SO) or sulfonyl (═SO₂) derivatives thereof, removed from suchhydrocarbon stream. The sulfur compounds, or sulfinyl (═SO) or sulfonyl(═SO₂) derivatives thereof in the gas phase are contacted with asupported metal oxide catalyst, or with a bulk metal oxide catalyst inthe presence of oxygen for a time sufficient to convert at least aportion of the heterocyclic sulfur compounds, or the sulfinyl (═SO) orsulfonyl (═SO₂) derivatives thereof, to oxygenated products andsulfur-deficient hydrocarbons and recovering a hydrocarbon stream withsubstantially reduced sulfur separately from the oxygenated products.The process not only results in the removal of sulfur compounds fromsuch petroleum feedstocks, such as gasoline and diesel feedstocks, butactually provides for the efficient upgrading of various cyclic sulfurcompounds found in these petroleum feedstocks (e.g., C₂-C₅ saturatedcyclic-sulfur compounds, thiophenes, benzothiophenes anddibenzothiophenes) to valuable chemical products (C₂-C₅ hydrocarbonsand/or oxygenated hydrocarbons, maleic anhydride, phenol, benzoic acidand H₂SO₄ or elemental sulfur). The oxidative desulfurization processthus reduces the sulfur content of hydrocarbon streams without the needfor additional hydrogen consumption.

According to the present invention, the sulfur compound impurities foundin a gaseous hydrocarbon feed stream containing such sulfur impurities,especially refractory sulfur compounds such as thiophenes,benzothiophenes, and dibenzothiophenes and their higher boilingderivatives, or the sulfinyl (═SO) or sulfonyl (═SO₂) derivativesthereof, are contacted in the presence of oxygen with a supported metaloxide catalyst. A supported metal oxide catalyst comprises a metal oxidesupport having supported thereon a layer, preferably only a monolayer,of a catalytic metal oxide. The catalytic metal oxide layer supported bythe metal oxide support used in the process of the present invention istypically based on a metal selected from the group consisting oftitanium (Ti), zirconium (Zr), molybdenum (Mo), rhenium (Re), vanadium(V), chromium (Cr), tungsten (W), manganese (Mn), niobium (Nb), tantalum(Ta) and mixtures thereof. The metal oxide support for the supportedmetal oxide catalyst generally is selected from titania (TiO₂), silica(SiO₂), zirconia (ZrO₂), alumina (Al₂O₃), ceria (CeO₂), magnesia (MgO),niobia (Nb₂O₅), tantala (Ta₂O₅), manganates (MnO_(x)), lanthanum oxide(La₂O₃), tin oxide (SnO₂) and mixtures thereof. Generally, a support oftitania, zirconia, ceria, niobia, tin oxide or their mixture ispreferred.

As a general rule, titanium (Ti), zirconium (Zr), niobium (Nb), tantalum(Ta) and tungsten (W) should not be used as the sole catalytic specieswith a silica support, nor should the metal oxide support and thesupported metal oxide of the catalyst be the same.

In a generally less preferred alternative embodiment of the presentinvention, the process also can be carried out using a bulk metal oxidecatalyst wherein the bulk metal oxide, and especially the bulk mixedmetal oxide, is based on molybdates (Mo), chromates (Cr), vanadates (V),rhenates (Re), titanates (Ti), niobates (Nb), tantalates (Ta),tungstates (W), manganates (Mn) and mixtures thereof. Bulk metal oxidecatalysts based on molybdenum, chromium and vanadium are preferred.

The preferred supported metal oxide catalyst compositions (mono-layeredcatalysts) and the bulk metal oxide catalyst compositions, useful forpracticing the present invention, are known in the prior art, as aretheir methods of production.

DETAILED DESCRIPTION OF THE INVENTION

Hydrocarbon feedstocks suitable for treatment using the presentinvention are those petroleum-based feedstocks, which contain condensedring sulfur heterocyclic compounds. Such compounds are typically foundin petroleum streams boiling in the distillate range and higher.Non-limiting examples of such feedstocks include a catalytically crackedgasoline stream (e.g., cracked naphtha), generally from a fluidcatalytic cracker (FCC gasoline) or thermal catalytic cracker (TCC), aheavy straight run gasoline stream, generally obtained by atmosphericdistillation of a crude, an aromatic saturated gasoline stream, dieselfuels and jet fuels. Such feeds typically have a boiling range fromabout 150 to about 600° C., usually from about 175 to about 400° C. Inthe broad practice of this invention, any hydrocarbon stream containingrefractory sulfur compounds can be treated, since their boiling pointtemperatures at atmospheric pressure are: thiophene (84° C.),2,5-dimethylthiophene (134° C.), 1-benzothiophene (222° C.),dibenzothiophene (333° C.), 4-methyldibenzothiophene (298° C.) and4,6-dimethyldibenzothiophene (estimated to be ˜250-380° C.).

There is a well-established hierarchy in the ease of sulfur removal fromthe various organo-sulfur compounds common to petroleum streams. Simplealiphatic mercaptans, naphthenic mercaptans, and aromatic mercaptans,sulfides, di-sulfides and polysulfides and the like generally surrendertheir sulfur content more readily than the class of heterocyclic sulfurcompounds comprised of thiophene and its higher homologs and analogs.Within the generic thiophenic class, desulfurization reactivity alsodecreases with increasing molecular structure and complexity. Whilesimple thiophenes represent the more labile sulfur types in this class,the other extreme, which is sometimes referred to as “hard sulfur” or“refractory sulfur,” is represented by the derivatives of benzothiopheneand dibenzothiophene, especially those mono-substituted anddi-substituted and condensed ring dibenzothiophenes. An example of atypical three-ring “hard” sulfur compound found in petroleum streams is4,6-dimethyldibenzothiophene, or 4,6-DMDBT for short. These highlyrefractory sulfur heterocycles resist desulfurization as a consequenceof steric inhibition. For this reason, these materials often survivetraditional desulfurization processes, e.g. hydrodesulfurization, andremain in the hydrocarbon stream as a potential poison for subsequentprocesses whose operability is dependent upon a sulfur sensitivecatalyst. Destruction of these “hard sulfur” types can be accomplishedunder relatively severe process conditions in HDS, but this isundesirable owing to the onset of harmful side reactions leading to feedand/or product degradation and excessive hydrogen consumption.

While the desulfurization process of the present invention ispotentially applicable to all sulfur bearing compounds common topetroleum streams, it is particularly suitable for the oxidativedesulfurization of the least reactive, more highly refractory sulfurspecies, such as those derived from thiophenes, benzothiophenes anddibenzothiophenes. As used throughout the specification and claims,therefore, the term “refractory sulfur” and similar terms is intended toembrace thiophene, benzothiophene, dibenzothiophene, and the higherboiling derivatives of these sulfur compounds. In addition, to thesesulfur compounds, the present invention also embraces the sulfinyl (═SO)or sulfonyl (═SO₂) derivatives of thiophene, benzothiophene,dibenzothiophene, and their higher boiling derivatives.

The process of the present invention generally will result in ahydrocarbon stream with substantially reduced sulfur, a sulfur dioxidestream and separate streams of oxygenated hydrocarbon products. Forpurposes of this invention, the term, “substantially reduced sulfur”,depends upon the overall process being considered, but can be defined asa sulfur content less than about 100 wppm, preferably less than about 50wppm, more preferably less than about 30 wppm, and most preferably lessthan about 10 wppm as measured by existing, conventional analyticaltechnology.

In accordance with the present invention, and with reference to FIG. 1,a sulfur-containing hydrocarbon gas stream 10, preferably containing andenriched amount of refractory sulfur compounds such as thiophene,benzothiophene, dibenzothiophene and their higher boiling derivatives,is introduced into a reactor 60. The level of such sulfur compounds canbe enriched in such steam using known techniques of absorption,adsorption, extraction and the like. Air or an oxygen-enriched gasgenerally is added via stream 20 to establish oxidizing conditions inreactor 60. Reactor 60 contains a supported metal oxide catalyst(preferably mono-layered), or a bulk metal oxide catalyst, in a formsuitable for conducting the oxidation reactions. The selective oxidationthat occurs in reactor 60 produces a gas stream containing theoxygenated hydrocarbon products, sulfur dioxide, H₂O, CO_(x) andunreacted hydrocarbons and sulfur compounds, which exits reactor 60 ingas stream 30. The oxygenated products may include maleic anhydride,phenol, benzyl aldehyde, benzoic acid and the like depending upon thenature of the sulfur compounds in gas stream 10.

As noted, the oxidizing agent used in the selective oxidation canusually be oxygen or air. The contacting of the, sulfur-containinghydrocarbon gas stream with the supported metal oxide catalyst or bulkmetal oxide catalyst under an oxidizing atmosphere, e.g., in thepresence of oxygen, and at an appropriate temperature, causes aselective oxidation of the sulfur compounds to the valuable oxygenatedproducts and sulfur deficient hydrocarbons.

The optimum reaction time in reaction zone 60 (space velocity) varieswith temperature, pressure and the molar ratio of the reactants. Thespace velocity likely will be maintained below about 4800 V/V/hr. As ageneral rule, higher conversions are associated with lower spacevelocities, e.g., a space velocity of 5 to 200 volume of gas (STP) pervolume of catalyst per hour. In the broad practice of the invention,space velocities of up to 2000 volumes of gas (STP) per volume ofcatalyst per hour are generally contemplated.

A variety of oxygenated species, such as maleic anhydride, phenol,benzyl aldehyde and benzoic acid, are the intended products of thepresent process and can be recovered from the gaseous reaction productvia stream 40, separate from byproduct SO₂ and the CO_(x) via stream 80and separate from unreacted (sulfur depleted) hydrocarbons andunconverted sulfur-containing compounds via stream 70, using any one ofa number of separation options (zone 50) known to those skilled in theart.

The selectivity of the oxidation of the organosulfur compounds to thevaluable oxygenated products and the sulfur-deficient hydrocarbons hasits origin in the preferential attack of oxygen at the C—S bonds of theorganosulfur compounds, in the vicinity of the catalytic surface sites,because of the weak C—S bonds relative to strong C—O bonds. The natureof the products resulting from the gas phase oxidation suggests that theinitial oxygen atoms are attached to the carbon atoms adjacent to thesulfur atom and that the thiomaleic anhydride can be completelyconverted to maleic anhydride at conversions approaching 100%.Over-oxidation of maleic anhydride to COx and H₂O should not be asignificant problem since anhydrides are known to be relatively stable(especially compared to the reactive C—S—C bond in thiomaleicanhydride).

Maleic anhydride, expected to be produced by the selective oxidation ofthiophene and some of the higher refractory sulfur compounds, is animportant chemical intermediate that is currently produced by selectiveoxidation of n-butane over bulk VPO catalysts, with annual production ˜2billion pounds. Phenol, another of the expected products from theselective oxidation of benzothiophene, ranks third among the secondaryproducts of benzene, one of the world's ten top bulk organic chemicals,and annual synthetic phenol production is ˜5 billion pounds. The currenttechnology to synthesize phenol from benzene is very complicated andconsumes much energy and produces significant waste by-products. Forexample, phenol production via the classical benzenesulfonic acidprocess yields 1.35 pounds of Na₂SO₃ and 2.1 pounds Na₂SO₄ asby-products for every pound of phenol. Moreover, a three-stagedistillation is required for phenol purification. The present process,thus provides a useful alternative source of this valuable chemical.Benzyl aldehyde, benzoic acid and maleic anhydride may also form frombenzothiophene.

Saturated cyclic sulfides are expected to be converted to dialdehydesand glycols (via hydrogenation), which also are valuable chemicalintermediates. Of special interest is the saturated C₂ cyclic sulfide,which should be oxidized to C₂-dialdehyde and can be hydrogenated toethylene glycol, ˜7 billion pounds annual production. The saturated C₅cyclic sulfide also is expected to be oxidized to maleic anhydride sincen-pentane is oxidized to maleic anhydride.

As will be recognized by those skilled in the art, the gas stream 30leaving the reactor will contain the hydrocarbon feedstock and maycontain unreacted sulfur compounds, as well as the oxygenated products,sulfur dioxide, carbon oxides and water. Principal by-products of theoxidative desulfurization that may be formed are carbon monoxide, whichmay be accompanied by carbon dioxide (possibly in a minor amount) andsulfur dioxide. COS may also be a minor product.

The reaction mixture leaving the reactor 60 in gas stream 30 isgenerally subject to further processing in zone 50 in a conventionalmanner. For example, a concentrated stream of the oxygenated products 40can be recovered in a washer, or by indirect cooling, or also byfractional cooling. For example, the washing can be performed with anaqueous stream, in which case a multi-stage washer can be used. Anaqueous stream 40 containing the oxygenated products can be obtained inthis manner separate from the sulfur dioxide and carbon oxides in stream80. An advantage of the vapor-phase route is the ease with which SO₂ andCO_(x) can be separated from the reaction products because of their veryhigh vapor pressure and any residual SO₂ can be readily removed with anion exchange column. With judicious selection of metal oxide catalyst,the sulfur-containing compounds that are typically present in petroleumfeedstocks and other petroleum products are expected to be selectivelyoxidized to valuable chemical intermediates or sulfur-deficienthydrocarbons.

The sulfur dioxide can be disposed of by any technique known in the art.For example, the sulfur oxide (from stream 80) can be oxidized andconverted to sulfuric acid. The sulfuric acid can then be used directlyin the petroleum refinery for purposes well known to those skilled inthe art. The crude stream 40 of the oxygenated products then can betreated, such as by distillation, for recovering a purified stream of,for example, maleic anhydride and other oxygenated species. Fractionalcondensation also can be used to obtain a desired oxygenated product.Other ways for individually isolating the oxygenated products will beapparent to those skilled in this art. The residual gas 80, likelycontaining carbon monoxide as well, may be treated (so as to recoversulfur oxides). The remaining fraction in stream 70 containing theoriginal hydrocarbon fraction and any unreacted sulfur compounds can berecycled to the oxidative desulfurization reactor 60 (not shown)following any heating that may be needed to convert the stream into agas, or may be sufficiently low in sulfur to be returned to the refineryfor use as a gasoline feed stock.

For obtaining higher yields and selectivities, the conditions of theoxidative desulfurization can be varied. For example, the pressure,temperature, composition of the starting gas mixture, the amount ofcatalyst and/or the rate of flow can be varied. The reactor effluentremaining after separation of the oxygenated products and by-productscan then be recycled (not shown) into the reactor 60.

A key feature of the present invention is the use of a heterogeneous gasphase reaction conducted in the presence of certain metal oxidesupported catalysts (preferably mono-layered catalysts), or bulk metaloxide catalysts, between the sulfur compounds and oxygen. The metaloxide of the supported metal oxide catalyst is accommodated in thesupport primarily as a two-dimensional metal oxide overlayer (preferablya mono-layer), with the oxide having a non-crystalline form. Supportedmetal oxide catalysts useful in the process of this invention generallycomprise a metal oxide substrate, or support, such as titania, silica,zirconia, alumina, niobia, tantala, ceria, magnesia, manganates,lanthanum oxide, tin oxide and mixtures thereof, whose surface has beenmodified with a layer (preferably no more than a monolayer) of an oxideof a catalytic metal or a mixture of catalytic metal oxides asidentified above (e.g., preferably an oxide of vanadium, and oxidemixtures containing vanadium) in an amount such that the catalystexhibits properties different from the metal oxide substrate whosesurface has not been modified. The support and the supported metalshould not be the same.

Consequently, in this preferred embodiment of the invention, the metaloxide loading (preferably vanadium oxide) on the metal oxide support orsubstrate, e.g., a titania support, must be sufficient to modify themetal oxide surface. The metal oxide loading on the metal oxide supportor substrate broadly ranges between about 0.5 to 35 wt % of the totalcatalyst weight.

The preferred vanadia (vanadium oxide) on titania, supported metal oxidecatalyst used in this process has at least a portion, preferably atleast about 25 wt %, and most preferably substantially all of saidsupported vanadium oxide in a non-crystalline form.

A preferred metal oxide support for use in the process of this inventionis titania (titanium dioxide), which can be employed in the anatase orrutile form. For example at least about 25 wt % (and generally fromabout 50 to about 100 wt %) of the titanium dioxide (TiO₂) can be in theanatase form. As recognized by those skilled in the catalytic art, thetitania support material needs to be judiciously evaluated since certaingrades may have impurities that interfere with the catalytic activity.Normally, with recognition of the previous caveat, the titanium dioxidemay be prepared by any conventional technique. The titanium dioxide usedin the catalyst of this invention may be composed of substantiallyporous particles of a diameter of from about 0.4 to about 0.7 micron andpreferably has a specific surface area of at least about 1 m²/g, moreusually at least about 5 m²/g, preferably at least about 40 m²/mg andsometimes at least about 100 m²/g.

The metal oxide supported catalysts used in the process of thisinvention may be prepared by impregnation techniques well-known in theart, such as incipient wetness, grafting, equilibrium adsorption, vapordeposition, thermal spreading, etc. When using an incipient wetnessimpregnation technique, an aqueous or non-aqueous solution containing ametal oxide precursor compound is contacted with the metal oxide supportor substrate material, e.g., titania, for a time sufficient to deposit ametal oxide precursor material onto the support such as by selectiveadsorption or alternatively, excess solvent may be evaporated leavingbehind the precursor compound or salt. If an incipient wetnessimpregnation technique is used to prepare a catalyst of this invention,the metal oxide precursor (e.g., salt) solution used may be aqueous ororganic, the only requirement being that an adequate amount of aprecursor compound for the selected metal oxide be soluble in thesolvent used in preparing this solution. Other impregnation techniques,such as vapor deposition and thermal spreading, do not require use of asolvent as does incipient wetness, and may be desirable in somecircumstances to avoid the problem of volatile organic carbon (VOC)emissions.

One way to disperse vanadium oxide, tungsten oxide or a combination ofthe two oxides onto a titania metal oxide support or substrate is toimpregnate titania spheres or powder (spheres or powder are used asrepresentative examples of shapes of titania) with a solution containinga vanadium or a tungsten compound. When impregnating a substrate withboth oxides, the tungsten and vanadium are introduced in a stepwisemanner, tungsten first, followed by vanadium, with appropriateintermediate drying and calcining steps. Each solution may be an aqueoussolution, one using an organic solvent or a mixture of the two.Generally, an aqueous solution is preferred. Criteria used to choose thevanadium and tungsten compounds include whether the compounds aresoluble in the desired solvent and whether the compounds decompose at anacceptable rate at a high, calcination temperature to give theappropriate metal oxide overlayer. Illustrative of suitable compounds ofvanadium and tungsten are the halides of vanadium and tungsten,oxyacids, oxyacid salts and oxysalts of vanadium and tungsten. Specificexamples or precursors are tungsten dibromide, tungsten pentabromide,tungsten tetrachloride, tungsten dioxydichloride, tungstic acid,ammonium meta-tungstate, vanadium tribromide, vanadium dichloride,vanadium trichloride, vanadium oxychloride, vanadium oxydichloride,vanadic acid, vanadyl sulfate, vanadium alkoxides, vanadium oxalate(which may be formed in situ by reaction of V₂O₅ and an aqueous solutionof oxalic acid), and ammonium meta-vanadate. Suitable metal oxideprecursor compounds for the other metal species suitable for making thesupported metal oxide catalysts of this invention are well recognized bythose skilled in the catalysis art.

The impregnation of the metal oxide support or substrate, e.g., titaniasupport in the form of spheres or powder, with the metal oxide precursorcompound solution may be carried out, as noted above, in ways well knownin the art using either wet or dry impregnation techniques. Oneconvenient method is to place the metal oxide support or substrate,e.g., titania particles, into a rotary evaporator, which is equippedwith a steam jacket. An impregnating solution of a precursor compoundwhich contains an amount of the desired metal to be included in thefinished catalyst (as the metal oxide) is added to the support particlesand the mixture is cold rolled (no steam) for a time from about 10 to 60minutes sufficient to impregnate the support with the precursor compoundsolution. Next, steam is introduced and the solvent is evaporated fromthe impregnated solution. This usually takes from about 1 to about 4hours. The impregnated support will normally be dried at temperaturesranging from about 50°-300° C. to remove excess solvent.

Water-soluble precursor compounds are generally preferred for industrialapplications because of the environmental concern about VOC emissions.Nonetheless, when using an organic solvent, initial heating may be donein a nitrogen atmosphere to remove any flammable solvent. Finally, thesupport particles are removed from the rotary evaporator and calcined ina suitable oxidizing atmosphere such as air, oxygen, etc. at atemperature of about 150° to 800° C., and more usually from 400°-600°C., preferably for about 1 to about 3 hours, sufficient to decompose theprecursor compound to the corresponding metal oxide. In other cases, asrecognized by those skilled in the art, calcining conditions need to beadjusted to avoid undesirably reducing the surface area of the metaloxide support.

Because some precursor compounds are air/moisture sensitive, they areprepared under a nitrogen atmosphere as is recognized by those skilledin this art. The time required to calcine the composite will, of course,depend on the temperature and in general will range from about 0.5-7hours. Calcination at 450° C. for about 2 hours has proven to besuitable for 1% vanadia on titania catalysts. The precise time andtemperature for calcination depends on the particular metal oxideoverlayer and should be selected, as well-recognized by those skilled inthe art, to avoid adversely affecting the metal oxide support, e.g. inthe case of a titania metal oxide support, to avoid substantial crystalphase transformation of the anatase into another crystalline form, e.g.,rutile, and degradation of extended surface area.

Reducing atmospheres may also be used to decompose the transition metaloxide precursors. To avoid potential safety concerns, the resultingcomposite should be calcined to convert the reduced metal component tothe oxide form. If the support is to be provided with an overlayer of acombination of metal oxides, e.g., if an overlayer containing bothvanadium oxide and tungsten oxide is desired, then the metal oxideprecursor compounds may be impregnated on the metal oxide supportsimultaneously, but preferably are impregnated sequentially. The metaloxide supported catalysts used in the process of this invention willgenerally have surface metal oxide loadings of from about 0.5 to 35 wt.% metal oxide based on the total active catalyst composition, preferablyfrom about 1 to 20 wt. %, more usually from about 1-15 wt. %, and mostpreferably 1-10 wt. % based on the total active catalyst composition.The intent, generally, is to provide no more than a monolayer of thecatalytic oxide overlayer on the metal oxide support.

Titania, silica, zirconia, alumina, niobia, tantala, ceria, magnesia,manganates, lanthanum oxide and tin oxide are conveniently referred toas supports or substrates in the description of the preferred embodimentof the present invention, based to a large degree on the way thecatalyst is prepared. Nonetheless, it should be noted that these metaloxides also provide important roles as active catalytic components inthe supported metal oxide catalyst. Combination supports may also beadvantageous for use in catalysts suitable for practicing the process ofthis invention. For example, substrates constituting a mixture oftitania and zirconia, or titania and silica can be used.

Further details on the preparation and structure of such metal oxidesupported catalysts useful in the practice of the present invention canbe found, inter alia, in Jehng et al., Applied Catalysis A, 83, (1992)179-200; Kim and Wachs, Journal of Catalysis, 142, 166-171; Jehng andWachs, Catalysis Today, 16, (1993) 417-426; Kim and Wachs, Journal ofCatalysis, 141, (1993) 419-429; Deo et al., Applied Catalysis A, 91,(1992) 27-42; Deo and Wachs, Journal of Catalysis, 146, (1994) 323-334;Deo and Wachs, Journal of Catalysis, 146, (1994) 335-345; Jehng et al.,J. Chem. Soc. Faraday Trans., 91(5), (1995) 953-961; Kim et al. Journalof Catalysis, 146, (1994) 268-277; Banares et al., Journal of Catalysis,150, (1994) 407-420 and Jehng and Wachs, Catalyst Letters, 13, (1992)9-20, the disclosures of which are incorporated herein by reference.

For the supported metal oxide catalyst, the preferred vanadium oxide maypreferably be used in mixture with an oxide of one of molybdenum (Mo),tungsten (W), chromium (Cr), rhenium (Re), and manganese (Mn), supportedon titania or silica. In the case of a vanadia on silica catalyst, anadjuvant selected from the group consisting of an oxide of titanium,zirconium, cerium, tin, niobium and tantalum, should generally bepresent to enhance catalytic activity. A particularly preferredsupported metal oxide catalyst is one comprising a vanadia overlayer(monolayer) on a titania support.

It often is desired that the metal oxide support, such as titania,silica, zirconia, alumina, niobia, tantala, magnesia, ceria, manganates,lanthanum oxide, tin oxide, and their mixtures, used as a catalystsupport component in accordance with the present invention have asurface area in the range of about 1 to about 150 m²/g and higher. Thesematerials may be used in any configuration, shape or size, which exposestheir surface and any metal oxide overlayer dispersed thereon, to thegaseous stream passed in contact therewith. For example, these oxidesupports, such as titania can conveniently be employed in a particulateform or deposited (before or after impregnation with the metal oxideoverlayer) on a monolithic carrier or onto ceramic rings or pellets. Asparticles, the support, such as titania, can be formed in the shape ofpills, pellets, granules, rings, spheres and the like. Use of freeparticulates might be desirable when large catalyst volumes are neededor if the catalyst bed is operated in a fluidized state. A monolithicform, or deposition of the active catalyst on an inert ceramic supportmight be preferred in applications where catalyst movement is to beavoided because of concerns about catalyst attrition and dusting, and apossible increase in pressure drop across a particulate catalyst bed. Ina preferred approach, a metal oxide supported catalyst, such as avanadia on titania catalyst, may be deposited on a ceramic carrier suchas silicon carbide, silicon nitride, carborundum steatite, alumina andthe like, provided in the shape of rings or pellets. Typically, theactive catalyst will be applied to the inert ceramic support in anamount to provide 1 to 15% by weight of the supported catalyst.

As noted, the present invention also contemplates the use of bulk metaloxides as the catalyst for converting petroleum sulfur compounds intooxygenated products. Such bulk metal oxide catalysts generallyconstitute molybdates (Mo), chromates (Cr), vanadates (V), rhenates(Re), titanates (Ti), niobates (Nb), tantalates (Ta), tungstates (W),manganates (Mn) and mixtures thereof. Such metal oxides also contain awide variety of other metal species such as alkali metals (e.g., sodium(Na), lithium (Li), potassium (K) and cesium (Cs)), alkaline earthmetals (e.g., calcium (Ca), barium (Ba), and magnesium (Mg)) andtransition metals (e.g., copper (Cu), nickel (Ni), cobalt (Co), aluminum(Al), lead (Pb), bismuth (Bi), iron (Fe), zinc (Zn), cadmium (Cd),tellurium (Te), manganese (Mn)). Those skilled in the art recognize thewide variety of available bulk metal oxide catalysts.

Methods for making bulk metal oxide catalysts used in the presentinvention also are well known to those skilled in the art. Inparticular, the active catalyst can be prepared by physically blendingthe metal oxides, by coprecipitation from aqueous solutions containingsoluble compounds of the catalyst components in the desired molar ratioor by any other technique, which provides an intimate mixture of themetal oxide constituents. For example, an aqueous solution of awater-soluble molybdenum compound (ammonium heptamolybdate) is mixedwith a water-soluble iron compound (ferric chloride) to causecoprecipitation of both molybdenum and iron, using procedures well knownto those skilled in the art. The coprecipitate is washed, to eliminatethe soluble salts formed during the coprecipitation reactions, filtered,dried and calcined to convert the metal constituents to their activeiron molybdate (oxide) form. Those skilled in the art recognize avariety of water-soluble metal compounds that can be used to prepare theactive bulk metal catalyst. Alternatively, oxides of the respectivemetals may be ground together and calcined. Additional details on bulkmetal oxides and bulk metal oxide catalysis can be found in Arora etal., Journals of Catalysis, 159, (1996) 1-13, which is incorporatedherein by reference.

Those skilled in the art recognize that there exists a wide range ofcompounds, generally used in admixture, suitable for preparing bulkmetal oxide catalysts. The following is a representative, though notexhaustive, list of possible constituents: bulk vanadates such asPbV₂O₆, NaVO₃, Na₃VO₄, BiVO₄ and other Bi—V—O family members, AlVO₄,FeVO₄, Mg₃(VO₄)₂, Mg₂V₂O₇, CeVO₄, Zn₃(VO₄)₂, CdV₂O₇, Zn₂V₂O₇, VOPO₄ andother V—P—O family members, KVO₃, Pb₂V₂O₇, and TIVO₄; bulk molybdatessuch as PbMoO₄, CaMoO₄, Bi₂Mo₂O₉, Bi₃(FeO₄)(MoO₄)₃ and other Bi—Mo—Ofamily members, Na₂MoO₄, MnMoO₄, Gd₂(MoO₄)₃, MgMoO₄, CuMoO₄, CoMoO₄,Fe₂(MoO₄)₃, Te₂MoO₇, NiMoO₄, Al₂(MoO₄)₃, Cr₂(MoO₄)₃, and Na₂Mo₂O₇; bulkniobates such as YNbO₄, YbNbO₄, LiNbO₃, NaNbO₃, KNbO₃, AlNbO₄, K₈Nb₆O₁₉,BiNbO₄, and other Bi—Nb—O family members, SbNbO₄, NbOPO₄, CaNb₂O₆,K₄Nb₆O₁₇, and KCa₂Nb₃O₁₀; bulk tungstates such as Li₆WO₆, FeWO₄, CoWO₄,MnWO₄, NiWO₄, CuWO₄, CaWO₄, Cs₂WO₄, Na₂WO₄, B_(a)WO₄, Fe₂(WO₄)₃,Al₂(WO₄)₃, SrWO₄, K₂WO₄, Na₂W₂O₇, Li₂WO₄, CsLuW₂O₈, BiWO₄, and otherBi—W—O family members; bulk chromates such as Na₂CrO₄, Na₂Cr₂O₇,Na₂Cr₃O₁₀, Na₂Cr₄O₁₃, K₂CrO₄, K₂Cr₂O₇, K₂Cr₃O₁₀, K₂Cr₄O₁₃, Fe₂(CrO₄)₃,CaCrO₄, Cs₂CrO₄; BiCrO₄ and other Bi—Cr—O family members; bulk rhenatessuch as NaReO₄, Li₆ReO₄, and Mg(ReO₄)₂; bulk titanates such as Na₂TiO₄,NaTiO₃, BaTiO₄, BaTiO₃, and other Ba—Ti—O as well as Bi—Ti—O familymembers and bulk manganates such as Mn₃(VO₄)₂, MnAl₂O₄, KMnO₄, MnO,MnO₂, Mn₂O₃, and Mn₃O₄.

To achieve high selectivity in the conversion of the petroleum sulfurcompounds to the oxygenated compounds, it is important to maintain theflow rate of reactant gas per unit mass of catalyst in the range of 10⁻²to 10⁴ cubic centimeters (STP) of reactants per gram of active catalystper minute (excluding inert ceramic components or other inert supportmaterial). Generally, higher reaction temperatures permit higher flowrates. Usually, the process can be operated at 10⁻¹ to 10², cubiccentimeters (STP) of reactants per gram of catalyst per minute.

The oxidation reaction involving the noted refractory sulfur compoundsis exothermic. As recognized by those skilled in the art a variety ofreactor designs may be employed, such as a tubular reactor, toaccommodate the necessary mass and heat transfer processes for effectiveoperation on a continuous basis, semi-continuous or batch basis. Packedcatalyst beds and fluid bed operation are contemplated as possibleembodiments. The oxidation reaction may be conducted at atmospherepressure, and above or below atmospheric pressure.

Among the aromatic heterocyclic sulfur compounds of particular interestin this application are thiophene, 2-methylthiophene, 3-methylthiophene,2-ethylthiophene, benzothiophene, and dimethylbenzothiophene, as well ashigher boiling derivatives. Mercaptans which can also be removed by theprocess of this invention often contain from 3-10 carbon atoms, and areillustrated by materials such as 1-mercaptopropane, 2-mercaptopropane,1-mercaptobutane, 2-mercaptobutane, 2-methyl-2-mercaptopropane,mercaptopentanes, mercaptohexanes, mercaptoheptanes, mercaptooctanes,mercaptononanes, and mercaptodecanes. The total sulfur content inhydrocarbon feedstocks usually is in the range from about 150 ppm to asmuch as several thousand ppm and higher. Indeed, hydrocarbon streamscontaining as much as 5% sulfur are often encountered. After treatmentaccording to the invention the sulfur content of the hydrocarbon streamis desirably no more than about 100 ppm, and more desirably under about50 ppm.

In another embodiment of the invention, the hydrocarbon stream,containing the organo-sulfur compounds may first be treated to reduceits sulfur content using an alternative technology, as shown in FIG. 2,before employing the oxidative desulfurization of the present invention.The stream may be treated to reduce its sulfur content preferably toless than about 1,000 ppm, more preferably to less than about 500 ppm,and most preferably to less than about 200 ppm before subjecting thehydrocarbon to the oxidative desulfurization of the present invention.It may be advantageous for the refiner to upgrade the sulfur-containingpetroleum feedstocks before treatment using the present invention byfirst removing as much as possible of the easy-to-remove sulfur usingconventional processes such as HDS.

In accordance with this embodiment of the present invention, and withreference to FIG. 2, a sulfur-containing hydrocarbon gas stream 10containing organo-sulfur compounds is first treated using an alternativesulfur removal system, such as conventional HDS, in treatment zone 100.As recognized by those skilled in the art, when using HDS thesulfur-containing petroleum feedstock is treated with a stream ofhydrogen (stream 20) to convert the easy-to-remove sulfur compounds tohydrogen sulfide (stream 30). Suitable processes for desulfurizinghydrocarbons, particularly gasoline feedstocks, include technologiesdescribed in the following U.S. Pat Nos. 5,340,466; 5,346,609;5,409,596; 5,411,658; 5,482,617; 5,500,108; 5,510,016; 5,510,568;5,525,210; 5,595,634; 5,597,476; 5,770,46; 5,807,477; 5,906,730;6,042,719; 6,103,105; 6,120,679; 6,153,089 and 6,162,352. Still othertechniques will be apparent to those skilled in the art of sulfurremoval. The easy-to-remove sulfur compounds include aliphaticmercaptans, naphthenic mercaptans, and aromatic mercaptans, sulfides,di-sulfides and polysulfides

The petroleum feedstock discharged from treatment zone 100, having areduced sulfur content, but retaining most, if not all, of therefractory sulfur compounds such as thiophene, benzothiophene,dibenzothiophene and their higher boiling derivatives, in stream 40 isthen preferably introduced into a concentration zone 200 for increasingthe concentration of such refractory sulfur compounds. For example, in apreferred approach the refractory sulfur compounds would be concentratedfrom the major portion of the petroleum feedstock, possibly viacomplexation with ammonium complexes or by use of another knownextraction or absorption technology, and distilled, or otherwiseseparated into a sulfur-concentrated hydrocarbon stream 60 and asulfur-depleted petroleum feedstock 50.

The sulfur concentrated hydrocarbon stream 60 then is introduced into areactor 600 for oxidative desulfurization. Air or an oxygen-enriched gasgenerally is added to the reactor via stream 70 to establish oxidizingconditions in reactor 600. Reactor 600 contains a supported metal oxidecatalyst, or a bulk metal oxide catalyst, in a form suitable forconducting the oxidation reactions. The selective oxidation that occursin reactor 600 produces a gas stream containing the oxygenated products,sulfur dioxide, H₂O, CO_(x) and unreacted hydrocarbons and sulfurcompounds, which exits reactor 600 in gas stream 80. The oxygenatedproducts may include maleic anhydride, phenol, benzyl aldehyde, benzoicacid and the like depending upon the nature of the sulfur compounds ingas stream 60 and sulfur-deficient hydrocarbons may also be produced.

As noted, the oxidizing agent used in the selective oxidation canusually be oxygen or air. The contacting of the sulfur-containinghydrocarbon gas stream with the supported metal oxide catalyst or bulkmetal oxide catalyst under an oxidizing atmosphere, e.g., in thepresence of oxygen, and at an appropriate temperature, causes aselective oxidation of the sulfur compounds to the valuable oxygenatedproducts.

The optimum reaction time in reaction zone 600 (space velocity) varieswith temperature, pressure and the molar ratio of the reactants. Thespace velocity likely will be maintained below about 4800 V/V/hr. As ageneral rule, higher conversions are associated with lower spacevelocities, e.g., a space velocity of 5 to 200 volume of gas (STP) pervolume of catalyst per hour. In the broad practice of the invention,space velocities of up to 2000 volumes of gas (STP) per volume ofcatalyst per hour are generally contemplated.

A variety of oxygenated species, such as maleic anhydride, phenol,benzyl aldehyde and benzoic acid, are the intended products of thepresent process and can be recovered from the gaseous reaction productstream 80, separate from byproduct SO₂ and the CO_(x) and from unreactedhydrocarbons, sulfur-deficient hydrocarbons and unconvertedsulfur-containing compounds (stream 110), using any one of a number ofseparation options known to those skilled in the art.

As will be recognized by those skilled in the art, the gas stream 80leaving the reactor will contain the hydrocarbon feedstock and maycontain unreacted sulfur compounds, sulfur-deficient hydrocarbons aswell as the oxygenated products, sulfur dioxide, carbon oxides andwater. Principal by-products of the oxidative desulfurization that maybe formed are carbon monoxide, which may be accompanied by carbondioxide (often in a minor amount) and sulfur dioxide.

The reaction mixture leaving the reactor 600 in gas stream 80 isgenerally subject to further processing in zone 500 in a conventionalmanner. For example, a concentrated stream of the oxygenated products 90can be recovered in a washer, or by indirect cooling, or also byfractional cooling. For example, the washing can be performed with anaqueous stream, in which case a multi-stage washer can be used. Anaqueous stream 90 containing the oxygenated products can be obtained inthis manner separate from the sulfur dioxide and carbon oxides in stream112. An advantage of the vapor-phase route is the ease with which SO₂and CO_(x) can be separated from the reaction products because of theirvery high vapor pressure and any residual SO₂ can be readily removedwith an ion exchange column. With judicious selection of metal oxidecatalyst, the sulfur-containing compounds that are typically present inpetroleum feed stocks are expected to be selectively oxidized tovaluable chemical intermediates and sulfur-deficient hydrocarbons.

The sulfur dioxide can be disposed of by any technique known in the art.For example, the sulfur oxide (from stream 112) can be oxidized andconverted to sulfuric acid. The sulfuric acid can then be used directlyin the petroleum refinery for purposes well known to those skilled inthe art. The crude stream of the oxygenated products then can betreated, such as by distillation, for recovering a purified stream of,for example, maleic anhydride. Fractional condensation also can be usedto obtain a desired oxygenated product. Other ways for isolating theoxygenated products will be apparent to those skilled in this art. Theresidual gas 112, likely containing carbon monoxide as well may betreated (so as to recover sulfur oxides). The remaining fraction instream 110 containing the hydrocarbon fraction and any unreacted sulfurcompounds and sulfur-deficient hydrocarbons can be recycled to theoxidative desulfurization reactor 600 (not shown) following any heatingthat may be needed to convert the stream into a gas, or may besufficient low in sulfur impurities to be returned to the refinery asfor blending with other feedstocks for making gasoline.

For obtaining higher yields and selectivities, the conditions of theoxidative desulfurization can be varied. For example, the pressure,temperature, composition of the starting gas mixture, the amount ofcatalyst and/or the rate of flow can be varied. The reactor effluentremaining after separation of the oxygenated products and by-productscan then be recycled (not shown) into the reactor 600.

In accordance with this invention, the refractory sulfur compounds areseparated and then isolated from a petroleum feedstock by distillation,solvent extraction and/or adsorption-desorption and then they areoxidized by gas phase oxidation over a supported metal oxide catalyst.In a particularly preferred embodiment of the present invention, shownschematically in FIG. 3, a sulfur-containing hydrocarbon gas stream 10containing organo-sulfur compounds is first treated using an alternativesulfur removal system, such as conventional HDS, in treatment zone 100.As recognized by those skilled in the art, when using HDS the,sulfur-containing petroleum feedstock is treated with a stream ofhydrogen (stream 20) to convert the easy-to-remove sulfur compounds tohydrogen sulfide (stream 30). Suitable processes for desulfurizinghydrocarbons, particularly gasoline feedstocks, include technologiesdescribed in the following U.S. Pat. Nos. 5,340,466; 5,346,609;5,409,596; 5,411,658; 5,482,617; 5,500,108; 5,510,016; 5,510,568;5,525,210; 5,595,634; 5,597,476; 5,770,46; 5,807,477; 5,906,730;6,042,719; 6,103,105; 6,120,679; 6,153,089 and 6,162,352. Still othertechniques will be apparent to those skilled in the art of sulfurremoval. The easy-to-remove sulfur compounds include aliphaticmercaptans, naphthenic mercaptans, and aromatic mercaptans, sulfides,di-sulfides and polysulfides. Alternatively, the easy-to-remove sulfurcompounds may also be desulfurized by oxidative desulfurization.

The petroleum feedstock discharged from treatment zone 100, having areduced sulfur content, but retaining most, if not all, of therefractory sulfur compounds such as thiophene, benzothiophene,dibenzothiophene and any higher boiling derivatives, in stream 40 isthen preferably introduced into a concentration zone 200 for isolatingthe sulfur compounds from the hydrocarbon stream. For a petroleumfeedstock that is already substantially free of the easy-to-removeorgano-sulfur compounds, i.e., contains only refractory sulfurcompounds, the stream can by-pass treatment zone 100 and be introduceddirectly into concentration zone 200.

For example, in a preferred approach for concentration zone 200 therefractory sulfur compounds could be isolated from the major portion ofthe petroleum feedstock, possibly via reversible complexation withammonium complexes or by use of another known extraction or absorptiontechnology, such as the extraction technique described in U.S. Pat. No.5,753,103 (the full disclosure of which is incorporated herein byreference), the ionic liquid extraction technique described by Bösmannet al., in Chem. Commun., 2001, 2492-2495 (the full disclosure of whichis incorporated herein by reference), or by a reversible olefincomplexation, such as by modifying the OATS process (for OlefinicAlkylation of Thiophenic Sulphur) developed and commercialized by BP.

The OATS process facilitates the separation of the thiophenes (and otherrefractory sulfur compounds) by catalytically causing them to react witholefins present in a hydrocarbon stream to produce heavier compoundswith boiling points above 200° C. In such modification, thesulfur-olefin complex would be broken, likely by heating the complex toisolate the organo-sulfur compounds.

In any event, following such processing in concentration zone 200, astream containing principally the refractory sulfur compounds such asthiophene, benzothiophene, dibenzothiophene and their higher boilingderivatives, is produced within concentration zone 200 and exits thatzone in stream 60.

In an alternate approach, the organo-sulfur compounds, principallyincluding refractory sulfur compounds such as thiophene, benzothiophene,dibenzothiophene and their higher boiling derivatives, may first betreated using a mild selective oxidation, such as a liquid phaseoxidation, to convert such organo-sulfur compounds to their sulfinyl(═SO) (sulfone) or sulfonyl (═SO₂) (sulfoxide) derivatives. Such mildoxidation processes are well known in the art These sulfinyl (═SO)(sulfone) or sulfonyl (═SO₂) (sulfoxide) derivatives then could beisolated, such as by extraction using dimethyl sulfoxide, or bydistillation or adsorption, and then would be subjected to furtherprocessing in accordance with the present invention.

Aside from the sulfur-containing feed stream 40 and the concentratedsulfur product steam 60, other feed streams and by-product streamsentering and exiting concentration zone 200 are not shown.

In yet another alternative arrangement, the OATS process could be usedto treat the original hydrocarbon stream 10 and then the lower boilingsulfur fraction recovered from that processing operation (e.g.,mercaptans, sulfides and the like) could be removed by fractionation andadded to other refinery streams, slated to be treated only byconventional hydrotreatment. The remaining fraction would lead to stream60 containing principally the refractory sulfur compounds such asthiophene, benzothiophene, dibenzothiophene, their higher boilingderivatives, or the sulfinyl (═SO) (sulfone) or sulfonyl (═SO₂)(sulfoxide) derivatives thereof

The refractory sulfur compounds, or the sulfinyl (═SO) (sulfone) orsulfonyl (═SO₂) (sulfoxide) derivatives thereof, in stream 60 are thenintroduced into a distillation zone 500 within which the variousfractions of the stream are separated using standard rectificationtechniques. For illustrative purposes only, stream 60 is shown beingseparated into three fractions 65 a, 65 b and 65 c, respectivelycontaining primarily thiophene, benzothiophene and higher boilingcompounds and derivatives, or their corresponding sulfinyl (═SO)(sulfone) or sulfonyl (═SO₂) (sulfoxide) derivatives. Each purifiedsteam then is introduced respectively into a reactor 600 a through 600 cfor oxidative desulfurization in accordance with the present invention.Air or an oxygen-enriched gas generally is added to each of the reactorsvia streams 70 a through 70 c respectively to establish oxidizingconditions in each respective reactor 600 a through 600 c. Each reactorpreferably contains a supported metal oxide catalyst (monolayercatalyst), or alternatively a bulk metal oxide catalyst, in a formsuitable for conducting the oxidation reactions. Each reactor can besimilar to those described above.

The selective oxidation that occurs in each reactor produces a gasstream containing the oxygenated product generated by oxidation of eachof the respective sulfur compounds, sulfur dioxide, H₂O, and CO_(x),which exits each reactor 600 a through 600 c in gas streams 80 a, 80 band 80 c respectively. The oxygenated products may include maleicanhydride in stream 80 a, phenol in stream 80 b, benzyl aldehyde andbenzoic acid in stream 80 c and the like, depending upon the nature ofthe sulfur compounds in each of the gas streams 60 a through 60 c.

As noted, the oxidizing agent used in the selective oxidation canusually be oxygen or air. The contacting of the organo-sulfur compounds,in the gaseous phase, with the supported metal oxide catalyst or bulkmetal oxide catalyst under an oxidizing atmosphere, e.g., in thepresence of oxygen, and at an appropriate temperature, causes aselective oxidation of the sulfur compounds to the valuable oxygenatedproducts.

Each oxidized product stream 80 a through 80 c then is treated in aseparation zone 700 a through 700 c to remove sulfur dioxide and otherlight boiling fractions from the desired oxygenated products in stream90 a through 90 c respectively.

The only significant emission from the process of the present inventionwould be undesirable greenhouse gas CO₂ due to minor unselectiveoxidation reaction pathways, as the sulfur dioxide can be recovered andused in the refinery as described above. Furthermore, the oxidativedesulfurization of the present invention removes the need for additionalhydrogen production from the costly and energy intensive methanereforming reaction, which would be required to support the plannedexpansion of the current hydrodesulfurization (HDS) technology to obtainthe higher level of sulfur removal required by the more stringentregulatory limits.

The vapor-phase organo-sulfur oxidation route of the present inventionis generally preferred relative to the known liquid oxidation approachesgiven the potential for large-scale production of the previouslydescribed oxygenated compounds, which are useful chemical intermediates.In addition, vapor-phase routes also avoid problems with solvents andcatalyst recovery usually encountered with liquid-phase oxidationprocesses and the mild temperatures employed in liquid-phase oxidation,which tend to yield only sulfoxides and sulfones.

The advantages offered by this oxidative desulfurization process are:(1) the use of free O₂, rather than expensive H₂ to drive thedesulfurization, (2) the elimination of, or diminution of the need forcostly reactor units for methane steam reforming and water-gas shift foradded hydrogen generation and for additional Claus reactions, (3) theproduction of significantly lower amounts of global warming CO₂ due tothe minor unselective oxidation reaction pathways, (4) the directproduction of H₂SO₄ that can be used in the alkylation processes in thepetroleum refinery and (5) the production of a supply of relativelyinexpensive sulfur-containing feedstocks for the production of valuablechemical intermediates as well as sulfur-deficient olefinic and aromatichydrocarbons. Thus, the oxidative desulfurization process of theinvention is able to remove sulfur from fuels in a way that approachesthe ultimate pollution control strategy: an environmentally benignprocess with zero emissions.

EXAMPLES

To facilitate a more complete understanding of the invention, a numberof examples showing catalyst preparation are provided below. The scopeof the invention, however, is not limited to specific embodimentsdisclosed in these examples, which are for purposes of illustrationonly.

Catalyst Preparation and Characterization—Supported metal oxidecatalysts can be prepared as follows:

Preparation Example 1 Vanadia on Titania

A vanadia on titania metal oxide supported catalyst can be prepared inaccordance with the following procedure. A vanadia-titania catalyst canbe prepared by using TiO₂ (Degussa P25) as the support. The TiO₂ support(˜10% rutile and ˜90% anatase) possesses a surface area of ˜55 m²/g. Itis calcined in air at 500° C. and cooled to room temperature beforeimpregnation with the vanadium oxide precursor. The vanadium oxideoverlayer on the TiO₂ support is prepared from vanadium triisopropoxideoxide (Alfa, 95-98% purity) by the incipient wetness impregnationmethod. The preparation is performed under a nitrogen environment and innonaqueous solutions, since the alkoxide precursor is air and moisturesensitive. Solutions of known amounts of vanadium triisopropoxide oxideand propanol-2, corresponding to the incipient wetness impregnationvolume and the final amount of vanadium required, are prepared in aglove box filled with nitrogen. The solutions of the vanadium precursorand propanol-2 are then thoroughly mixed with the titania support anddried at room temperature in the glove box for 24 hr. The impregnatedsamples are heated to 300° C. in flowing nitrogen and the finalcalcination is performed in O₂ (Linde, 99.9% pure) at 500° C. for 15hours. The catalyst is then pelletized, crushed and sieved to obtaincatalyst particles sizes between 100 to 200 μm.

Preparation Example 1A Vanadia on Titania

Another vanadia on titania metal oxide supported catalyst can beprepared using the general procedure of Preparation Example 1 exceptthat the final calcination is conducted at 450° C. for 2 hours.

Preparation Example 2 Molybdenum Oxide on Titania

An aqueous solution of ammonium heptamolybdate ((NH₄)₆Mo₇O₂₄.4H₂O)(Alfa) is deposited onto TiO₂ (Degussa P25) as the support (˜10% rutileand ˜90% anatase) by the incipient wetness technique. As in Example 1,the support is calcined in air at 500° C. and cooled to room temperaturebefore impregnation with the molybdenum oxide precursor. The supportpossesses a surface area of ˜55 m²/g. After impregnation, the wetsamples are dried at room temperature for 16 hours, further dried at110-120° C. for 16 hours and calcined at 450° C. for 12 hours. Thecatalyst is then pelletized, crushed and sieved to obtain catalystparticles sizes between 100 to 200 μm.

Preparation Example 3 Chromia on Titania

An aqueous solution of chromium nitrate (Cr(NO₃)₃.9H₂O) (Allied ChemicalCo.) is deposited onto TiO₂ (Degussa P25) as the support using theincipient wetness technique. As in the previous Examples, the TiO₂support (˜10% rutile and ˜90% anatase) is calcined in air at 500° C. andcooled to room temperature before impregnation with the chromiumprecursor. The support possesses a surface area of ˜55 m²/g. Afterimpregnation, the wet samples are dried at room temperature for 16hours, further dried at 110-120° C. for 16 hours and calcined at 450° C.for 13 hours. The catalyst is then pelletized, crushed and sieved toobtain catalyst particles sizes between 100 to 200 μm.

Preparation Example 4 Rhenium Oxide on Titania

An aqueous solution of perrhenic acid (HReO₄) (Aldrich) is depositedonto TiO₂ (Degussa P25) as the support using the incipient wetnesstechnique. As before, the TiO₂ support (˜10% rutile and ˜90% anatase) iscalcined in air at 500° C. and cooled to room temperature beforeimpregnation with the rhenium oxide precursor. The support possesses asurface area of ˜55 m²/g. After impregnation, the wet samples are driedat room temperature for 16 hours, further dried at 110-120° C. for 16hours and calcined at 450° C. for 13 hours. The catalyst is thenpelletized, crushed and sieved to obtain catalyst particles sizesbetween 100 to 200 μm.

Preparation Example 5 Vanadia on Zirconia

A vanadium oxide overlayer is deposited onto a zirconium oxide (ZrO₂)support (Degussa) having a surface area ˜39 m²g⁻¹ using an organicsolution of vanadium triisopropoxide oxide (Alfa, 95-98% purity). Inparticular, the vanadium overlayer is prepared by the incipient wetnessimpregnation method using a solution of vanadium triisopropoxide oxideand propanol-2 in a glove box filled with nitrogen. The solutions of thevanadium precursor and propanol-2 are thoroughly mixed with the zirconiasupport and dried at room temperature for 16 hours, further dried at110-120° C. for 16 hours and calcined at 450° C. for 16 hours. Thecatalyst is then pelletized, crushed and sieved to obtain catalystparticles sizes between 100 to 200 μm.

Preparation Example 6 Vanadia on Niobia

A vanadium oxide overlayer is deposited on a niobia (Nb₂O₅) support (55m²g⁻¹) using vanadium triisopropoxide oxide (Alfa, 95-98% purity) andthe incipient wetness technique. The niobia support is prepared bycalcining niobic acid (Niobia Products Co.) at 500° C. for two hours. Asolution of vanadium triisopropoxide oxide and propanol-2 is thoroughlymixed with the niobia support in a glove box filled with nitrogen, driedat room temperature for 16 hours, further dried at 110-120° C. for 16hours and calcined at 450° C. for 16 hours. The catalyst is thenpelletized, crushed and sieved to obtain catalyst particles sizesbetween 100 to 200 μm.

Preparation Example 7 Vanadia on Alumina

A vanadium oxide overlayer is deposited on an alumina (Al₂O₃) support(Harshaw, 180 m²g⁻¹) using an organic solution of vanadiumtriisopropoxide oxide (Alfa, 95-98% purity) and the incipient wetnessimpregnation. A solution of the vanadium precursor and propanol-2 isthoroughly mixed with the alumina support, in a glove box filled withnitrogen, dried at room temperature for 16 hours, further dried at110-120° C. for 16 hours and calcined at 500° C. for 16 hours. Thecatalyst is then pelletized, crushed and sieved to obtain catalystparticles sizes between 100 to 200 μm.

Preparation Example 8 Vanadia on Silica

A vanadium oxide overlayer is deposited on a silica (SiO₂) support(Cab-O-Sil, 300 m²g⁻¹) using an organic solution of vanadiumtriisopropoxide oxide (Alfa, 95-98% purity) and the incipient wetnessimpregnation. A solution of the vanadium precursor and propanol-2 isthoroughly mixed in a glove box filled with nitrogen with the SiO₂support, the wet silica was dried at room temperature for 16 hours,further dried at 110-120° C. for 16 hours and calcined at 500° C. for 16hours. The catalyst is then pelletized, crushed and sieved to obtaincatalyst particles sizes between 100 to 200 μm.

Preparation Example 9 Tungsten Oxide on Silica

An aqueous solution of ammonium metatungstate ((NH₄)₆H₂W₁₂O₄₀.xH₂O)(Pfaltz & Bauer, 99.9% purity) is deposited as an oxide overlayer onto asilica (SiO₂) support (Cab-O-Sil, 300 m²g⁻¹) using the incipient wetnesstechnique. After impregnation, the silica support is dried at roomtemperature for 16 hours, further dried at 110-120° C. for 16 hours andcalcined at 500° C. for 16 hours. The catalyst is then pelletized,crushed and sieved to obtain catalyst particles sizes between 100 to 200μm.

Preparation Example 10 Niobia on Silica

An aqueous solution of niobium oxalate (Niobium Products Co.) isdeposited onto a silica (SiO₂) support (Cab-O-Sil, 300 m²g⁻¹) using theincipient wetness technique. After impregnation, the silica support isdried at room temperature for 16 hours, further dried at 110-120° C. for16 hours and calcined at 500° C. for 16 hours. The catalyst is thenpelletized, crushed and sieved to obtain catalyst particles sizesbetween 100 to 200 μm.

Preparation Example 11 Titania on Silica

Titanium isopropoxide (Aldrich) in a toluene solution is impregnatedonto a silica (SiO₂) support (Cab-O-Sil, 300 m²g⁻¹) under a nitrogenblanket to form a titania overlayer using the incipient wetnesstechnique. After impregnation, the wet silica is dried at roomtemperature for 16 hours, further dried at 110-120° C. for 16 hours andcalcined at 500° C. for 16 hours. The catalyst is then pelletized,crushed and sieved to obtain catalyst particles sizes between 100 to 200μm.

Preparation Example 12 Vanadia and Tungsten Oxide on Titania

A vanadia and tungsten oxide on titania catalyst is prepared by a twostep incipient wetness impregnation method. A vanadium oxide overlayeris deposited first on the TiO₂ support using a solution of vanadiumtriisopropoxide oxide (Alfa, 95-98% purity) and propanol-2 by theincipient wetness impregnation method in a glove box filled withnitrogen. The solution of the vanadium precursor and propanol-2 arethoroughly mixed with the TiO₂ (Degussa P25) as the support. The TiO₂support (˜10% rutile and ˜90% anatase) is prepared by previouscalcination in air at 500° C. and cooled to room temperature beforeimpregnation with the vanadium oxide precursor. The support possesses asurface area of ˜55 m²/g. After impregnation, the wet TiO₂ is dried atroom temperature for 16 hours, further dried at 110-120° C. for 16 hoursand calcined at 450° C. for 12 hours. Subsequently, an aqueous solutionof ammonium metatungstate ((NH₄)₆H₂W₁₂O₄₀.xH₂O) is deposited as an oxideoverlayer onto the TiO₂ support, again using the incipient wetnesstechnique. After impregnation, the wet samples are dried at roomtemperature for 16 hours, further dried at 110-120° C. for 16 hours andcalcined at 500° C. for 16 hours. The catalyst is then pelletized,crushed and sieved to obtain catalyst particles sizes between 100 to 200μm.

Preparation Example 13 Vanadia and Titania on Silica

A vanadia and titania on silica catalyst is prepared by a two stepincipient wetness impregnation method. The silica support used for thisstudy was Cabosil EH-5 (380 m²/g). This fluffy material is treated withwater in order to condense its volume for easier handling. Then the wetSiO2 is dried at 120° C. and subsequently calcined at 500° C. overnight.A titanium oxide overlayer is deposited first on the silica (SiO₂)support under a nitrogen blanket using titanium isopropoxide (Aldrich)in a toluene solution by the incipient wetness impregnation method in aglove box filled with nitrogen. After impregnation, the loaded sample isdried at room temperature for 16 hours, further dried at 110-120° C. for16 hours and calcined at 500° C. for 4 hours. Subsequently, a solutionof vanadium triisopropoxide oxide (Alfa, 95-98% purity) and propanol-2is impregnated onto the silica (SiO₂) support containing titania againusing the incipient wetness technique. The solution of the vanadiumprecursor and propanol-2 is thoroughly mixed with the SiO₂ supportcontaining titania. After impregnation, the wet SiO₂ is dried at roomtemperature for 16 hours, further dried at 110-120° C. for 16 hours andcalcined at 450° C. for 2 hours. The catalyst is then pelletized,crushed and sieved to obtain catalyst particles sizes between 100 to 200μm.

Example 1

Temperature Programmed Surface Reaction Mass Spectrometry (TPSR-MS) wascarried out with an AMI-100 system (Zeton Altamira Instruments) equippedwith an online mass spectrometer (Dycor DyMaxion, Ametek ProcessInstruments). The catalyst sample (200 mg of a 5% V₂O₅/TiO₂) was loadedin an U-type quartz tube and pretreated at 450° C. in flowing dry airfor 1 h to remove moisture and ensure the catalyst was fully oxidized,and then cooled down to the adsorption temperature in He (Air gas,ultrahigh purity) flow. The temperature was probed using a thermocoupleplaced ˜5 mm above the top portion of the catalyst bed. The adsorptionwas performed at 50° C. for thiophene by flowing a certified mixture of1000 ppm Thiophene/He (Scott Specialty Gases) for 30 minutes at a flowrate of 30 mL/min. After the reactor was purged of any excess adsorbentswith He for 30 minutes the catalyst was then ramped from the adsorptiontemperature to 500° C. at a constant heating rate of 10° C./min in He or5% O₂/He (Scott Specialty Gases) with a flow rate of 30 mL/min. Thedesorbed gases were analyzed by a quadruple mass spectrometer linked viaa capillary tube from the exiting gas stream of the reactor at m/e=26(Maleic Anhydride) and m/e=64 (SO₂), respectively. Pure gases of He andAr were used to verify the calibration of the mass spectrometer prior toany analysis.

The results are shown in FIG. 4. The separate figures show thedesorption of maleic anhydride and SO₂ after adsorption of thiophene ona 5% V₂O₅/TiO₂ catalyst at 100 C. The sample is heated at a rate of 10C/minute in flowing oxygen/He and the reaction products are monitored bya mass spectrometer. This transient experiment proves that maleicanhydride can be formed from thiophene oxidesulfurization on supportedvanadia on titania catalyst. The first plot (for maleic anhydride) showsthe formation of maleic anhydride from thiophene under the statedconditions. The second plot (for SO2) shows that the sulfur contained inthe thiophene ring has been removed as SO₂ during the formation ofmaleic anhydride mentioned earlier.

Another product from the oxidation was n-butane, a sulfur-deficienthydrocarbon, as is shown in FIG. 5.

It will be understood that while the invention has been described inconjunction with specific embodiments thereof, the foregoing descriptionand examples are intended to illustrate, but not limit the scope of theinvention. Other aspects, advantages and modifications will be apparentto those skilled in the art to which the invention pertains, and theseaspects and modifications are within the scope of the invention, whichis limited only by the appended claims.

1. A process for desulfurizing a hydrocarbon stream containingheterocyclic sulfur compounds, which process comprises contacting saidheterocyclic sulfur compounds, or sulfinyl (═SO) or sulfonyl (═SO₂)derivatives thereof, in the gas phase and in the presence of oxygen witha supported metal oxide catalyst, or with a bulk metal oxide catalyst.2. The process of claim 1 wherein the contacting converts at least aportion of the heterocyclic sulfur compounds, or the sulfinyl (═SO) orsulfonyl (═SO₂) derivatives thereof, to oxygenated products.
 3. Theprocess of claim 1 wherein the contacting converts at least a portion ofthe heterocyclic sulfur compounds, or the sulfinyl (═SO) or sulfonyl(═SO₂) derivatives thereof, to oxygenated products and then recovering ahydrocarbon stream with substantially reduced sulfur separately from theoxygenated products.
 4. The process of claim 1 wherein the contactingconverts at least a portion of the heterocyclic sulfur compounds, or thesulfinyl (═SO) or sulfonyl (═SO₂) derivatives thereof, tosulfur-deficient hydrocarbons.
 5. The process of claim 1 wherein thecontacting converts at least a portion of the heterocyclic sulfurcompounds, or the sulfinyl (═SO) or sulfonyl (═SO₂) derivatives thereof,to oxygenated products and sulfur-deficient hydrocarbons.
 6. The processof claim 1 wherein the contacting converts at least a portion of theheterocyclic sulfur compounds, or the sulfinyl (═SO) or sulfonyl (═SO₂)derivatives thereof, to oxygenated products and sulfur-deficienthydrocarbons and then recovering a hydrocarbon stream with substantiallyreduced sulfur separately from the oxygenated products.
 7. The processof claim 1, 2, 3, 4, 5 or 6 wherein the supported metal oxide catalystcomprises a metal oxide substrate, or support, such as titania, silica,zirconia, alumina, niobia, tantala, ceria, magnesia, manganates,lanthanum oxide, tin oxide and mixtures thereof, whose surface has beenmodified with a monolayer of an oxide of a catalytic metal selected fromthe group consisting of titanium (Ti), zirconium (Zr), molybdenum (Mo),rhenium (Re), vanadium (V), chromium (Cr), tungsten (W), manganese (Mn),niobium (Nb), tantalum (Ta) and mixtures thereof.
 8. The process ofclaim 7 wherein the catalytic metal is vanadium and mixtures containingvanadium.
 9. The process of claim 1, 2, 3, 4, 5 or 6 wherein the bulkmetal oxide catalyst comprises a compound selected from molybdates (Mo),chromates (Cr), vanadates (V), rhenates (Re), titanates (Ti), niobates(Nb), tantalates (Ta), tungstates (W), manganates (Mn) and mixturesthereof.
 10. The process of claim 8 wherein the bulk metal oxidecatalyst is selected from PbV₂O₆, NaVO₃, Na₃VO₄, BiVO₄ AlVO₄, FeVO₄,Mg₃(VO₄)₂, Mg₂V₂O₇, CeVO₄, Zn₃(VO₄)₂, CdV₂O₇, Zn₂V₂O₇, VOPO₄, KVO₃,Pb₂V₂O₇, TlVO₄, PbMoO₄, CaMoO₄, Bi₂Mo₂O₉, Bi₃(FeO₄)(MoO₄)₃, Na₂MoO₄,MnMoO₄, Gd₂(MoO₄)₃, MgMoO₄, CuMoO₄, CoMoO₄, Fe₂(MoO₄)₃, Te₂MoO₇, NiMoO₄,Al₂(MoO₄)₃, Cr₂(MoO₄)₃, Na₂Mo₂O₇, YNbO₄, YbNbO₄, LiNbO₃, NaNbO₃, KNbO₃,AlNbO₄, K₈Nb₆O₁₉, BiNbO₄, SbNbO₄, NbOPO₄, CaNb₂O₆, K₄Nb₆O₁₇, KCa₂Nb₃O₁₀,Li₆WO₆, FeWO₄, CoWO₄, MnWO₄, NiWO₄, CuWO₄, CaWO₄, Cs₂WO₄, Na₂WO₄,B_(a)WO₄, Fe₂(WO₄)₃, Al₂(WO₄)₃, SrWO₄, K₂WO₄, Na₂W₂O₇, Li₂WO₄ ,CsLuW₂O₈, BiWO₄, Na₂CrO₄, Na₂Cr₂O₇, Na₂Cr₃O₁₀, Na₂Cr₄O₁₃, K₂CrO₄,K₂Cr₂O₇, K₂Cr₃O₁₀, K₂Cr₄O₁₃, Fe₂(CrO₄)₃, CaCrO₄, Cs₂CrO₄, BiCrO₄,NaReO₄, Li₆ReO₄, Mg(ReO₄)₂, Na₂TiO₄, NaTiO₃, BaTiO₄, BaTiO₃, Mn₃(VO₄)₂,MnAl₂O₄, KMnO₄, MnO, MnO₂, Mn₂O₃ and Mn₃O₄.